Wireless power transmitter and wireless power receiver

ABSTRACT

An automatic tuning assist circuit is coupled in series with a transmission antenna. A first switch and a second switch are arranged in series between a first terminal and a second terminal of the automatic tuning assist circuit. Furthermore, a third switch and a fourth switch are arranged in series between the first terminal and the second terminal. A first auxiliary capacitor is arranged between a connection node that connects the first switch and the second switch and a connection node that connects the third switch and the fourth switch. A first control unit switches on and off the first switch through the fourth switch with the same frequency as that of the driving voltage, and with a given phase difference with respect to the driving voltage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless power supply technique.

2. Description of the Related Art

In recent years, wireless (contactless) power transmission has been receiving attention as a power supply technique for electronic devices such as cellular phone terminals, laptop computers, etc., or for electric vehicles. Wireless power transmission can be classified into three principal methods using an electromagnetic induction, an electromagnetic wave reception, and an electric field/magnetic field resonance.

The electromagnetic induction method is employed to supply electric power at a short range (several cm or less), which enables electric power of several hundred watts to be transmitted in a band that is equal to or lower than several hundred kHz. The power use efficiency thereof is on the order of 60% to 98%. In a case in which electric power is to be supplied over a relatively long range of several meters or more, the electromagnetic wave reception method is employed. The electromagnetic wave reception method allows electric power of several watts or less to be transmitted in a band between medium waves and microwaves. However, the power use efficiency thereof is small. The electric field/magnetic field resonance method has been receiving attention as a method for supplying electric power with relatively high efficiency at a middle range on the order of several meters (see Non-patent document 1).

[Non-Patent Document 1]

A. Karalis, J. D. Joannopoulos, M. Soljacic, “Efficient wireless non-radiative mid-range energy transfer” ANNALS of PHYSICS Vol. 323, January 2008, pp. 34-48

FIG. 1 is a diagram showing a wireless power transmission system according to a comparison technique. The wireless power transmission system 1 r includes a wireless power transmitting apparatus 2 r and a wireless power receiving apparatus 4 r. The wireless power transmitting apparatus 2 r includes a transmission coil L_(TX), a resonance capacitor C_(TX), and an AC power supply 10 r. The wireless power receiving apparatus 4 r includes a reception coil L_(RX), a resonance capacitor C_(RX), and a load 70.

The resonance frequency is an important factor in magnetic field (electric field) resonance power transmission. The resonance frequency of the transmitter side LC resonance circuit is represented by f_(TX)=1/(2π√(L_(TX)·C_(TX))). The resonance frequency of the receiver side LC resonance circuit is represented by f_(RX)=1/(2π√(L_(RX)·C_(RX))). Thus, in order to provide high-efficiency electric power transmission, there is a need to appropriately adjust the transmitter-side and receiver-side resonance frequencies and the frequency of the AC power supply 10 r. However, in actuality, such resonance frequencies fluctuate depending on various kinds of factors. It is difficult for the power receiving apparatus side to tune the fluctuating resonance frequency based on the magnetic field (or electric field) itself as it has been transmitted from the power transmitting apparatus. This is because, in some cases, the resonance frequency detected by the power receiving apparatus side further changes depending on the resonance frequency and the phase conditions of the power receiving apparatus side.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve such a problem. Accordingly, it is an exemplary purpose of an embodiment of the present invention to provide a wireless power transmitting apparatus, a wireless power receiving apparatus, and a wireless power supply system, which are capable of automatically tuning the resonance frequency.

An embodiment of the present invention relates to a wireless power transmitting apparatus configured to transmit an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field to a wireless power receiving apparatus. The wireless power transmitting apparatus comprises: a transmission antenna comprising a transmission coil; an automatic tuning assist circuit coupled with the transmission antenna; and a power supply configured to apply an AC driving voltage across a series circuit that comprises the transmission antenna and the automatic tuning assist circuit. The automatic tuning assist circuit comprises: a first terminal; a second terminal; a first switch and a second switch arranged in series between the first terminal and the second terminal; a third switch and a fourth switch sequentially arranged in series between the first terminal and the second terminal such that they are arranged on a path that is in parallel with the first switch and the second switch; a first auxiliary capacitor arranged between a connection node that connects the first switch and the second switch and a connection node that connects the third switch and the fourth switch; and a first control unit configured to switch on and off the first switch through the fourth switch in synchronization with the driving voltage.

When the frequency of the driving voltage does not match the resonance frequency of the resonance circuit including the transmission antenna, the resonance circuit functions as a capacitor circuit or otherwise an inductor circuit. In this case, in the transmission antenna, a resonance current is induced with a phase that is delayed or otherwise advanced with respect to the phase of the driving voltage. In this state, in a case in which the first switch through the fourth switch are switched on and off with a predetermined phase difference with respect to the driving voltage, the first auxiliary capacitor is charged or otherwise discharged so as to provide phase matching between the resonance current and the driving voltage. By applying the correction voltage that develops at the first auxiliary capacitor to the transmission antenna, such an arrangement provides a quasi-resonant state. Such an embodiment is capable of automatically tuning the transmission antenna with respect to the driving voltage even without an operation such as adjusting the capacitance of the resonance capacitor. It should be noted that, in the present specification, the “phase difference” may be set to zero. That is to say, examples of the “phase difference” state include a phase matching state.

Also, the first control unit may be configured to switch on and off each of the first switch through the fourth switch with the same frequency as that of the driving voltage, or otherwise with a frequency obtained by multiplying or dividing the frequency of the driving voltage by an odd number.

With an embodiment, the power supply may comprise: a DC power supply; and a first high-side switch and a first low-side switch sequentially arranged in series between an output terminal of the DC power supply and a fixed voltage terminal. Also, the transmission antenna and the automatic tuning assist circuit may be coupled in series between a connection node that connects the first high-side switch and the first low-side switch and the fixed voltage terminal.

With an embodiment, the power supply may comprise: a DC power supply; a first high-side switch and a first low-side switch sequentially arranged in series between an output terminal of the DC power supply and a fixed voltage terminal; and a second high-side switch and a second low-side switch sequentially arranged in series between the output terminal of the DC power supply and the fixed voltage terminal. Also, the transmission antenna and the automatic tuning assist circuit may be coupled in series between a connection node that connects the first high-side switch and the first low-side switch and a connection node that connects the second high-side switch and the second low-side switch. With an embodiment, the first switch through the fourth switch may each be configured as a uni-directional switch. Also, the first control unit may be configured to switch on and off the first switch through the fourth switch with a phase controlled such that no current flows through each of their inversely conducting elements.

With an embodiment, the first switch through the fourth switch may each be configured as a bi-directional switch.

With an embodiment, the automatic tuning assist circuit may be coupled in series with the transmission antenna via a transformer.

With an embodiment, the transmission antenna may comprise a resonance capacitor arranged in series with the transmission coil.

With an embodiment, the power supply may be configured to apply an AC driving voltage via a transformer across a series circuit that comprises the transmission antenna and the automatic tuning assist circuit.

Another embodiment of the present invention relates to a wireless power supply system. The wireless power supply system comprises: the wireless power transmitting apparatus according to any one of the aforementioned embodiments; and a wireless power receiving apparatus configured to receive an electric power signal from the wireless power transmitting apparatus.

Yet another embodiment of the present invention relates to a wireless power receiving apparatus configured to receive an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field, transmitted from a wireless power transmitting apparatus. The wireless power receiving apparatus comprises: a reception antenna comprising a reception coil; and an automatic tuning assist circuit coupled with the reception antenna. The automatic tuning assist circuit comprises: a first terminal; a second terminal; a fifth switch and a sixth switch arranged in series between the first terminal and the second terminal; a seventh switch and an eighth switch sequentially arranged in series between the first terminal and the second terminal such that they are arranged in parallel with the fifth switch and the sixth switch; a second auxiliary capacitor arranged between a connection node that connects the fifth switch and the sixth switch and a connection node that connects the seventh switch and the eighth switch; and a second control unit configured to switch on and off the fifth switch through the eighth switch.

When the frequency of the electric power signal does not match the resonance frequency of the resonance circuit including the reception antenna, the resonance circuit functions as a capacitor circuit or otherwise an inductor circuit. In this case, a resonance current flows through the resonance circuit with a phase that is delayed or otherwise advanced with respect to the phase of resonance voltage that is induced in the resonance circuit. In this state, in a case in which the fifth switch through the eighth switch are switched on and off, the second auxiliary capacitor is charged or otherwise discharged so as to provide phase matching between the resonance current and the resonance voltage. By applying the correction voltage that develops at the second auxiliary capacitor to the reception antenna, such an arrangement provides a quasi-resonant state. Such an embodiment is capable of automatically tuning the reception antenna with respect to the electric power signal even without an operation such as adjusting the capacitance of the resonance capacitor.

Also, the second control unit may be configured to switch on and off each of the fifth switch through the eighth switch with the same frequency as that of the electric power signal, or otherwise with a frequency obtained by multiplying or dividing the frequency of the electric power signal by an odd number.

With an embodiment, a load to which electric power is to be supplied may be connected to the second auxiliary capacitor.

With an embodiment, a load to which electric power is to be supplied may be connected to the reception antenna.

With an embodiment, the wireless power receiving apparatus may further comprise a transformer having a primary winding connected in series with the reception antenna. Also, a load to which electric power is to be supplied may be connected to a secondary winding of the transformer.

With an embodiment, the fifth switch through the eighth switch may each be configured as a uni-directional switch. Also, the second control unit may be configured to switch on and off the fifth switch through the eighth switch with a phase controlled such that no current flows through each of their inversely conducting elements.

With an embodiment, the fifth switch through the eighth switch may each be configured as a bi-directional switch.

With an embodiment, the second control unit may be configured to drive the fifth switch through the eighth switch with a predetermined phase difference with respect to a driving voltage applied to a transmission antenna of the wireless power transmitting apparatus.

With an embodiment, the automatic tuning assist circuit may be coupled in series with the reception antenna via a transformer.

With an embodiment, the reception antenna may comprise a resonance capacitor arranged in series with the reception coil.

Yet another embodiment of the present invention relates to a wireless power supply system. The wireless power supply system comprises: a wireless power transmitting apparatus configured to transmit an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field; and the wireless power receiving apparatus according to any one of the aforementioned embodiments, configured to receive the electric power signal.

Yet another embodiment of the present invention relates to an automatic tuning assist circuit employed in a wireless power transmitting apparatus, and coupled with the transmission coil. The automatic tuning assist circuit comprises: at least one auxiliary capacitor; four switches arranged in order to charge and discharge the aforementioned at least one auxiliary capacitor using a resonance current that flows through the transmission coil; and a first control unit configured to switch on and off the four switches so as to generate a capacitor voltage across the aforementioned at least one auxiliary capacitor, and to apply, to the transmission coil, a correction voltage that corresponds to the capacitor voltage that develops at the aforementioned at least one auxiliary capacitor.

By providing such an automatic tuning assist circuit, such an arrangement provides a quasi-resonant state. Thus, such an arrangement is capable of automatically tuning the transmission antenna with respect to the driving voltage even without an operation such as adjusting the capacitance of the resonance capacitor.

Yet another embodiment of the present invention relates to an automatic tuning assist circuit employed in a wireless power receiving apparatus, and coupled with the reception coil. The automatic tuning assist circuit comprises: at least one auxiliary capacitor; four switches arranged in order to charge and discharge the aforementioned at least one auxiliary capacitor using a resonance current that flows through the reception coil; and a second control unit configured to switch on and off the four switches so as to generate a capacitor voltage across the aforementioned at least one auxiliary capacitor, and to apply, to the reception coil, a correction voltage that corresponds to the capacitor voltage that develops at the aforementioned at least one auxiliary capacitor.

By providing such an automatic tuning assist circuit, such an arrangement provides a quasi-resonant state. Thus, such an arrangement is capable of automatically tuning the reception antenna with respect to the electric power signal even without an operation such as adjusting the capacitance of the resonance capacitor.

It is to be noted that any arbitrary combination or rearrangement of the above-described structural components and so forth is effective as and encompassed by the present embodiments.

Moreover, this summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:

FIG. 1 is a diagram showing a wireless power transmission system according to a comparison technique;

FIG. 2 is a circuit diagram showing a configuration of a wireless power transmitting apparatus according to a first embodiment;

FIGS. 3A through 3F are diagrams each showing an example configuration of a switch employing MOSFETs;

FIG. 4 is a waveform diagram showing the operation of the wireless power transmitting apparatus shown in FIG. 2;

FIG. 5 is an equivalent circuit diagram of the wireless power transmitting apparatus shown in FIG. 2;

FIG. 6A is a waveform diagram showing a state in which an automatic tuning assist circuit does not operate, and FIG. 6B is a waveform diagram showing a state in which the automatic tuning assist circuit operates;

FIG. 7 is a phasor diagram for describing a quasi-resonant state provided by the automatic tuning assist circuit in a case in which f_(c)<f_(TX);

FIG. 8 is a diagram showing a resonance current in a non-resonant state and in a resonance state;

FIG. 9 is a phasor diagram for describing a quasi-resonant state provided by the automatic tuning assist circuit in a case in which f_(c)>f_(TX);

FIG. 10 is a circuit diagram showing a configuration of a wireless power transmitting apparatus according to a first modification;

FIG. 11 is a circuit diagram showing a configuration of a wireless power transmitting apparatus according to a second modification;

FIG. 12 is a circuit diagram showing a configuration of a wireless power transmitting apparatus according to a third modification;

FIGS. 13A and 13B are circuit diagrams showing the configurations of wireless power transmitting apparatuses according to a fourth modification and a fifth modification, respectively;

FIG. 14 is a circuit diagram showing a configuration of a wireless power receiving apparatus according to the first embodiment;

FIG. 15 is an equivalent circuit diagram of the wireless power transmitting apparatus shown in FIG. 14;

FIG. 16 is a waveform diagram showing the operation of the wireless power receiving apparatus shown in FIG. 14;

FIGS. 17A and 17B are circuit diagrams showing the configurations of wireless power receiving apparatuses according to a first modification and a second modification;

FIG. 18 is a circuit diagram showing a configuration of a wireless power receiving apparatus according to a third modification;

FIGS. 19A and 19B are circuit diagrams showing the configurations of wireless power receiving apparatuses according to a fourth modification and a fifth modification, respectively;

FIG. 20 is a circuit diagram showing an example configuration of a wireless power transmission system according to the first embodiment;

FIG. 21 is a waveform diagram showing the operation of the wireless power transmission system shown in FIG. 20;

FIG. 22 is a circuit diagram showing a configuration of a wireless power receiving apparatus according to a second embodiment;

FIG. 23 is a waveform diagram showing the operation of the wireless power transmitting apparatus shown in FIG. 22;

FIG. 24 is a circuit diagram showing the configuration of a wireless power transmitting apparatus according to a first modification;

FIGS. 25A through 25C are circuit diagrams showing the configurations of wireless power transmitting apparatuses according to a second modification through a fourth modification, respectively;

FIG. 26 is a circuit diagram showing a configuration of a wireless power receiving apparatus according to the second embodiment;

FIG. 27 is a waveform diagram showing the operation of the wireless power receiving apparatus shown in FIG. 26;

FIGS. 28A and 28B are circuit diagrams showing the configurations of wireless power receiving apparatuses according to a second modification and a third modification, and FIGS. 28C and 28D are circuit diagrams each showing an example configuration of a load; and

FIG. 29 is a circuit diagram showing a configuration of a wireless power receiving apparatus according to a third modification.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on preferred embodiments which do not intend to limit the scope of the present invention but exemplify the invention. All of the features and the combinations thereof described in the embodiment are not necessarily essential to the invention.

In the present specification, the state represented by the phrase “the member A is connected to the member B” includes a state in which the member A is indirectly connected to the member B via another member that does not substantially affect the electric connection therebetween, or that does not damage the functions or effects of the connection therebetween, in addition to a state in which the member A is physically and directly connected to the member B.

Similarly, the state represented by the phrase “the member C is provided between the member A and the member B” includes a state in which the member A is indirectly connected to the member C, or the member B is indirectly connected to the member C via another member that does not substantially affect the electric connection therebetween, or that does not damage the functions or effects of the connection therebetween, in addition to a state in which the member A is directly connected to the member C, or the member B is directly connected to the member C.

First Embodiment [Wireless Power Transmitting Apparatus]

FIG. 2 is a circuit diagram showing a configuration of a wireless power transmitting apparatus 2 according to a first embodiment. The wireless power transmitting apparatus 2 transmits an electric power signal S1 to a wireless power receiving apparatus (not shown). As such an electric power signal 51, the wireless power transmitting apparatus 2 uses the near-field components (electric field, magnetic field, or electromagnetic field) of electromagnetic waves that have not yet become radio waves.

The wireless power transmitting apparatus 2 includes a power supply 10, a transmission antenna 20, an automatic tuning assist circuit 30, and a first control unit 40.

The transmission antenna 20 includes a transmission coil L_(TX) arranged between its first terminal 21 and its second terminal 22. A resonance capacitor C_(TX) is arranged in series with the transmission coil L_(TX). The resonance capacitor C_(TX) and the transmission coil L_(TX) may also be mutually exchanged.

The automatic tuning assist circuit 30 is coupled in series with the transmission antenna 20. The power supply 10 is applies an AC driving voltage V_(DRV) having a predetermined transmission frequency f_(TX) across a series circuit that comprises the transmission antenna 20 and the automatic tuning assist circuit 30. The driving voltage V_(DRV) may have a desired AC waveform, examples of which include a rectangular waveform, a trapezoidal waveform, a sine waveform, and the like. With the present embodiment, the driving voltage V_(DRV) is configured as a rectangular wave signal which swings between a first voltage level (power supply voltage V_(DD)) and a second voltage level (ground voltage V_(GND)=0 V). The power supply 10 includes a DC power supply 12, a first high-side switch SWH1, and a first low-side switch SWL1. The DC power supply 12 generates a DC power supply voltage V_(DD). The first high-side switch SWH1 and the first low-side switch SWL1 are sequentially connected in series between the output terminal of the DC power supply 12 and a fixed voltage terminal (ground terminal). The first control unit 40 switches on and off the first high-side switch SWH1 and the first low-side switch SWL1 in a complementary manner, with a transmission frequency f_(TX).

The automatic tuning assist circuit 30 includes a first terminal 31, a second terminal 32, a first switch SW1, a second switch SW2, and a first auxiliary capacitor C_(A1).

The first switch SW1 and the first auxiliary capacitor C_(A1) are arranged in series between the first terminal 31 and the second terminal 32. The first switch SW1 and the first auxiliary capacitor C_(A1) may also be mutually exchanged. The second switch SW2 is arranged in parallel with the first switch SW1 and the first auxiliary capacitor C_(A1) between the first terminal 31 and the second terminal 32. The first auxiliary capacitor C_(A1) is preferably configured to have a sufficiently greater capacitance than that of the resonance capacitor C_(TX).

The first control unit 40 switches on and off the first switch SW1 and the second switch SW2 in a complementary manner, with the same frequency f_(TX) as that of the driving voltage V_(DRV), and with a predetermined phase difference θ_(TX) with respect to the driving voltage V_(DRV). The phase difference θ_(TX) may preferably be set to a value in the vicinity of +90 degrees or otherwise −90 degrees (270 degrees). That is to say, a part of the first control unit 40 functions as a component of the automatic tuning assist circuit 30.

The first switch SW1 and the second switch SW2 are each configured employing a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), bipolar transistor, or the like. FIGS. 3A and 3B are diagrams each showing an example configuration of a switch employing a MOSFET.

FIG. 3A shows a configuration of the switch employing an N-channel MOSFET. FIG. 3B shows a configuration of the switch employing a P-channel MOSFET. In a case in which the back gate of the MOSFET is connected to its source, the body diode that forms between the back gate and the drain is in the connection state regardless of the gate voltage. Thus, such a switch configured as a single MOSFET is not capable of blocking a current that flows in one particular direction. In the present specification, such a switch will be referred to as a “uni-directional switch”.

The switches shown in FIGS. 3C through 3F each comprise two N-channel MOSFETs or otherwise two P-channel MOSFETs connected such that their body diodes are connected in reverse directions (back-to-back connection). With the switches shown in FIGS. 3C through 3F, in the off state, no current flows in either direction. In the present specification, such a switch will be referred to as a “bi-directional switch”.

With the present embodiment, the switches SW1 and SW2 may each be configured as a uni-directional switch or otherwise a bi-directional switch. It should be noted that, in a case in which the switches SW1 and SW2 are each configured as a uni-directional switch, there is a need to pay attention to their switching phases. Detailed description thereof will be made later.

The above is the configuration of the wireless power transmitting apparatus 2. Next, description will be made regarding the operation thereof.

Let us consider an arrangement in which the switches SW1 and SW2 are each configured as a bi-directional switch which is capable of blocking a current in both directions in the off state.

FIG. 4 shows waveform diagrams each showing the operation of the wireless power transmitting apparatus 2 shown in FIG. 2. FIG. 4 shows, in the following order beginning from the top, the voltage at the first high-side switch SWH1, the voltage at the first low-side switch SWL1, the driving voltage V_(DRV), the voltage at the first switch SW1, the voltage at the second switch SW2, the voltage V_(CA1) at the first auxiliary capacitor C_(A1), the voltage V_(A) at the first terminal 31, the resonance current I_(TX) that flows through the transmission antenna 20, and the resonance voltage V_(TX) that develops between the transmission coil L_(TX) side end and the resonance capacitor C_(TX) side end. In the waveform diagram for each switch, the high level represents the on state, and the low level represents the off state. It should be noted that FIG. 4 shows the waveforms of the resonance current I_(TX) and the resonance voltage V_(TX) obtained after a sufficient time has elapsed after the automatic tuning assist circuit 30 starts to operate.

As shown in FIG. 4, by switching on and off the first high-side switch SWH1 and the first low-side switch SWL1 in a complementary manner, such an arrangement is capable of generating the driving voltage V_(DRV) having a rectangular waveform. The driving voltage V_(DRV) thus generated is applied between the transmission antenna 20 side end and the automatic tuning assist circuit 30 side end. The first control unit 40 switches on and off the first switch SW1 and the second switch SW2 in a complementary manner, with the same frequency as that of the driving voltage V_(DRV), and with a phase that is delayed by θ_(TX) (=90 degrees) with respect to the driving voltage V_(DRV). The resonance current I_(TX) flows to the first auxiliary capacitor C_(A1) during the on time T_(ON1) of the first switch SW1, and flows to the ground via the second switch SW2 during the on time T_(ON2) of the second switch SW2. That is to say, the first auxiliary capacitor C_(A1) is charged and discharged by means of the resonance current I_(TX). As a result, the capacitor voltage V_(CA1) develops at the first auxiliary capacitor C_(A1).

The automatic tuning assist circuit 30 applies a correction voltage V_(A) to the second terminal 22 of the transmission antenna 20. During the on time T_(ON1) of the first switch SW1, the first auxiliary capacitor voltage V_(CA1) is used as the correction voltage V_(A). On the other hand, during the on time T_(ON2) of the second switch SW2, the ground voltage V_(GND) is used as the correction voltage V_(A). The automatic tuning assist circuit 30 can be regarded as a correction power supply configured to apply the correction voltage V_(A) to the transmission antenna 20. FIG. 5 is an equivalent circuit diagram showing an equivalent circuit of the wireless power transmitting apparatus 2 shown in FIG. 2.

FIG. 6A is a waveform diagram showing a state in which the automatic tuning assist circuit 30 does not operate, and FIG. 6B is a waveform diagram showing a state in which the automatic tuning assist circuit 30 operates.

First, description will be made with reference to FIG. 6A regarding the state in which the automatic tuning assist circuit 30 does not operate, i.e., a state in which the first switch SW1 is fixed to the off state, and the second switch SW2 is fixed to the on state. In this state, the correction voltage V_(A) is fixed to the ground voltage V_(GND).

The impedance Z of the transmission antenna 20 is represented by the following Expression (1). The resonance frequency f_(c) of the transmission antenna 20 is represented by the following Expression (2). The following Expressions (1) and (2) represent the impedance and the resonance frequency assuming that the resistance component is negligible. However, it is needless to say that, in actual circuits, the resistance component connected in series contributes to the circuit impedance.

Z=jωL _(TX)+1/(jωC _(TX))  (1)

f _(c)=1/2π√(L _(TX) ·C _(TX))  (2)

In a case in which the frequency f_(TX) of the driving voltage V_(DRV) is higher than the resonance frequency f_(c) (f_(TX)>f_(c)), the transmission antenna 20 functions as an inductor. In this case, the resonance current I_(TX) that flows through the transmission antenna 20 has a phase which is delayed with respect to the phase of the driving voltage V_(DRV). Conversely, in a case in which the frequency f_(TX) of the driving voltage V_(DRV) is lower than the resonance frequency f_(c) (f_(TX)<f_(c)), the transmission antenna 20 functions as a capacitor. In this case, the resonance current I_(TX) has a phase which is advanced with respect to the driving voltage V_(DRV).

FIG. 6A shows a state in which f_(c)>f_(TX). In this state, the resonance current I_(TX) has a phase which is advanced by the phase difference φ with respect to the driving voltage V_(DRV). It should be noted that the phase difference φ is not 90 degrees. This is because the resonance circuit includes a non-negligible resistance component (not shown) connected in series. In the non-resonant state, the impedance Z exhibits a high value, leading to a reduced amplitude of the resonance current I_(TX). In this state, such an arrangement is not capable of transmitting a large amount of electric power.

Next, description will be made with reference to FIG. 6B regarding a case in which the automatic tuning assist circuit 30 operates.

In a case in which the automatic tuning assist circuit 30 operates, the correction voltage V_(A) is applied to the transmission antenna 20 with a phase that is delayed by θ_(TX)=90 degrees with respect to the driving voltage V_(DRV). As a result, phase matching is obtained between the resonance current I_(TX) and the driving voltage V_(DRV), thereby providing a quasi-resonant state. In this state, the resonance current I_(TX) has a greater amplitude than that in the non-resonant state.

FIG. 7 is a phasor diagram (vector diagram) for describing the quasi-resonant state provided by the automatic tuning assist circuit 30.

The phase of the driving voltage V_(DRV) is 0 degrees. The phase of the correction voltage V_(A) is θ_(TX)=90 degrees. In a case in which f_(c)<f_(TX), the current has a phase that is delayed by the phase difference φ with respect to the voltage. Thus, the phase difference φ exists between the driving voltage V_(DRV) and the current component I_(DRV). Furthermore, the phase difference φ exists between the correction voltage V_(A) and the current component V_(A).

Based on the “principle of superposition”, the resonance current I_(TX) is configured as the sum of the current component I_(DRV) induced by the driving voltage V_(DRV) and the current component I_(A) induced by the correction voltage V_(A). There is a phase difference of θ_(TX) (=90 degrees) between the driving voltage V_(DRV) and the correction voltage V_(A). Accordingly, there is a phase difference of 90 degrees between the current components I=_(DRV) and I_(A). Thus, by optimizing the amplitude of the correction voltage V_(A), i.e., by optimizing the amplitude of the current component I_(A), such an arrangement is capable of providing phase matching between the driving voltage V_(DRV) (having a phase of 0 degrees) and a resultant current obtained by combining the two current components I_(DRV) and I_(A), i.e., the resonance current I_(TX). That is to say, it can be clearly understood that such an arrangement provides a quasi-resonant state.

The wireless power transmitting apparatus 2 according to the embodiment is capable of automatically generating the correction voltage V_(A) which provides the quasi-resonant state, which is an important excellent advantage of the wireless power transmitting apparatus 2 according to the embodiment.

FIG. 8 is a diagram showing the resonance current I_(TX) in the non-resonant state and in the resonance state. The waveform (I) represents the resonance current I_(TX) in the non-resonant state. In the on time T_(ON1) in which the switch SW1 is on, the first auxiliary capacitor C_(A1) is charged and discharged by means of the resonance current I_(TX). Specifically, the first auxiliary capacitor C_(A1) is charged during a period in which the resonance current I_(TX) is positive, and is discharged during a period in which the resonance current I_(TX) is negative. As a result, in a case in which the period in which the resonance current I_(TX) is positive is longer than the period in which the resonance current I_(TX) is negative, the capacitor voltage V_(CA1) rises. Otherwise, the capacitor voltage V_(CA1) drops.

Let us say that the capacitor voltage V_(CA1) rises in the on time T_(ON1) of a certain cycle. In this case, the correction voltage V_(A) is applied to the transmission antenna 20 according to the rising capacitor voltage V_(CA1). This advances the phase of the resonance current I_(TX) with respect to the resonance current I_(TX) of the previous cycle. By repeatedly performing this processing, the capacitor voltage V_(CA1) rises in increments of cycles, which gradually advances the phase of the resonance current I=. Eventually, the phase of the resonance current I_(TX) shifts until it matches the phase of the driving voltage V_(DRV) (resonance point). When the phase of the resonance current I_(TX) exceeds the resonance point, the discharge current of the first auxiliary capacitor C_(A1) becomes greater than its charging current, thereby providing a feedback control operation in the reverse direction. This reduces the capacitor voltage V_(CA1), thereby returning the phase of the resonance current I_(TX) to the resonance point. At the resonance point, such an arrangement provides a balance between the charging current and the discharging current of the first auxiliary capacitor C_(A1) for each cycle, thereby providing an equilibrium state of the capacitor voltage V_(CA1). In this state, a quasi-resonant state is maintained. As described above, with the wireless power transmitting apparatus 2 shown in FIG. 2, such an arrangement is capable of automatically generating the correction voltage V_(A) that is required to provide the quasi-resonant state.

The above is the operation of the wireless power transmitting apparatus 2.

As described above, without adjusting the resonance frequency f_(c) of the transmission antenna 20, the wireless power transmitting apparatus 2 is capable of automatically tuning the circuit state so as to provide the quasi-resonant state. In the wireless power transmission, the resonance frequency changes over time according to the position relation between the wireless power transmitting apparatus 2 and the wireless power receiving apparatus 4. The wireless power transmitting apparatus 2 is capable of following the change in the resonance frequency with high speed, thereby providing high-efficiency electric power transmission. Furthermore, in a case in which a large amount of electric power is transmitted by means of wireless power transmission, a very high voltage develops between both ends of the resonance capacitor C_(TX), which limits the use of a variable capacitor. With the wireless power transmitting apparatus 2, there is no need to adjust the capacitance of the resonance capacitor C_(TX). Thus, such an arrangement does not require such a variable capacitor or the like, which is another advantage.

Description has been made above regarding a case in which the first switch SW1 is switched on and off with a phase that is delayed by θ_(TX) (=90 degrees) with respect to the phase of the switching of the first high-side switch SWH1. However, the phase difference θ_(TX) between the first switch SW1 and the first high-side switch SWH1 is not restricted to 90 degrees. Also, an arrangement may be made in which the phase difference θ_(TX) between the first switch SW1 and the first high-side switch SWH1 is set to 270 degrees (−90 degrees). In this case, the capacitor voltage V_(CA1) is automatically adjusted such that it becomes a negative voltage.

That is to say, in a case in which f_(c)<f_(TX), by setting the phase difference θ_(TX) to 90 degrees or otherwise 270 degrees, such an arrangement provides a quasi-resonant state.

Also, the phase difference θ_(TX) may be moved away from 90 degrees or 270 degrees. In this case, the phase difference θ_(TX) between the current components I_(DRV) and I_(A) does not match 90 degrees. However, even in such a case, the capacitor voltage V_(CA1) is automatically adjusted such that the resultant resonance current I_(TX) has a phase of 0 degrees. It should be noted that, as the phase difference θ_(TX) becomes closer to 90 degrees or otherwise 270 degrees, the required value of the amplitude of the current component I_(A), i.e., the required absolute value of the capacitor voltage V_(CA1), becomes smaller. This is an advantage in employing an arrangement in which the phase difference θ_(TX) is set to 90 degrees or otherwise 270 degrees.

It should be noted that, in a case in which f_(c)<f_(TX), such an arrangement is capable of supporting the quasi-resonant state in which the phase difference θ_(TX) is set to 270 degrees only in a case in which the first switch SW1 and the second switch SW2 are each configured as a bi-directional switch. In other words, in a case in which the first switch SW1 and the second switch SW2 are each configured as a uni-directional switch, such an arrangement is not capable of supporting the quasi-resonant state in which the phase difference θ_(TX) is set to 270 degrees. This is because the current flows through the body diode. Thus, in a case in which the first switch SW1 and the second switch SW2 are each configured as a uni-directional switch, there is a need to switch on and off the first switch SW1 and the second switch SW2 with a phase such that no current flows through the body diodes which each function as an inversely conducting element.

The wireless power transmitting apparatus 2 automatically provides a quasi-resonant state not only in a case in which f_(c)<f_(TX), but also in a case in which f_(c)>f_(TX). In this case, the phase difference θ_(TX) is preferably set to 270 degrees (−90 degrees).

FIG. 9 is a phasor diagram for describing a quasi-resonant state provided by the automatic tuning assist circuit 30 in a case in which f_(c)>f_(TX). Description will be made below assuming that the driving voltage V_(DRV) has a phase of 0 degrees, and the correction voltage V_(A) has a phase θ_(TX) of 270 degrees (−90 degrees). In a case in which f_(c)>f_(TX), the current has a phase which is advanced with respect to that of the voltage. Such an arrangement also provides a quasi-resonant state even in such a case.

It should be noted that, in a case in which f_(c)>f_(TX), the phase difference θ_(TX) may be set to a value in the vicinity of 90 degrees. In this case, the capacitor voltage V_(CA1) is automatically adjusted such that it becomes a negative voltage so as to provide a quasi-resonant state.

It should be noted that, in a case in which f_(c)<f_(TX), such an arrangement is capable of supporting the quasi-resonant state in which the phase difference θ_(TX) is set to 90 degrees only in a case in which the first switch SW1 and the second switch SW2 are each configured as a bi-directional switch. In other words, in a case in which the first switch SW1 and the second switch SW2 are each configured as a uni-directional switch, such an arrangement is not capable of supporting the quasi-resonant state in which the phase difference θ_(TX) is set to 90 degrees. This is because the current flows through the body diode.

Next, description will be made regarding modifications of the wireless power transmitting apparatus 2. Each modification may be combined with any one of the other modifications, which is encompassed within the scope of the present invention.

Description has been made above regarding an arrangement in which the first control unit 40 drives multiple switches included in the automatic tuning assist circuit 30 with the same frequency f_(TX) as that of the driving voltage V_(DRV). However, the present invention is not restricted to such an arrangement. Also, the first control unit 40 may be configured to switch on and off the aforementioned switches with a frequency obtained by multiplying or dividing the frequency of the driving voltage V_(DRV) by an odd number. Such an arrangement also provides a quasi-resonant state.

FIG. 10 is a circuit diagram showing a configuration of a wireless power transmitting apparatus 2 a according to a first modification. An automatic tuning assist circuit 30 a includes a second auxiliary capacitor C_(A2) between the first terminal 31 and the second terminal 32 such that it is connected in series with the second switch SW2.

With such a modification, during the on time T_(ON1) of the first switch SW1, the correction voltage V_(A) is set to the capacitor voltage V_(CA1). During the on time T_(ON2) of the second switch SW2, the correction voltage V_(A) is set to the capacitor voltage V_(CA2).

With the wireless power transmitting apparatus 2 a, by optimizing the capacitor voltages V_(CA1) and V_(CA2), such an arrangement provides a quasi-resonant state both in the case in which V_(TX)>f_(c) and in the case in which V_(TX)<f_(c).

FIG. 11 is a circuit diagram showing a configuration of a wireless power transmitting apparatus 2 b according to a second modification. An automatic tuning assist circuit 30 b includes a charger circuit 34 and a detection resistor Rs. The detection resistor Rs is arranged on a path of the resonance current I_(TX). A detection voltage V_(S) develops at the detection resistor Rs in proportion to the resonance current I_(TX). The charger circuit 34 charges the first auxiliary capacitor C_(A1) based on the detection voltage V_(S) so as to provide a quasi-resonant state. As described above, the capacitor voltage V_(CA1) automatically becomes the optimum level. In addition, by providing the charger circuit 34, such an arrangement provides a quasi-resonant state in a shorter period of time.

FIG. 12 is a circuit diagram showing a configuration of a wireless power transmitting apparatus 2 c according to a third modification. Description has been made in which the power supply is configured as a half-bridge circuit. In contrast, a power supply 10 c shown in FIG. 12 is configured as an H-bridge circuit. A second high-side switch SWH2 and a second low-side switch SWL2 are sequentially connected in series between the output terminal of the power supply 12 and a fixed voltage terminal (ground terminal).

The first control unit 40 c repeatedly switches states between a state in which the pair of the high-side switch SWH1 and the second low-side switch SWL2 are turned on and a state in which the pair of the second high-side switch SWH2 and the first low-side switch SWL1 are turned on.

A driving voltage V_(DRV) that develop at a connection node (first output terminal) OUT1 that connects the first high-side switch SWH1 and the first low-side switch SWL1 has a phase that is the reverse of the phase of a driving voltage #V_(DRV) that develops at a connection node (second output terminal) OUT2 that connects the second high-side switch SWH2 and the second low-side switch SWL2. The transmission antenna 20 and an automatic tuning assist circuit 30 c are coupled in series between the first output terminal OUT1 and the second output terminal OUT2.

With the wireless power transmitting apparatus 2 c shown in FIG. 12, such an arrangement provides the same advantages as those provided by the wireless power transmitting apparatus described above.

FIGS. 13A and 13B are circuit diagrams showing the configurations of wireless power transmitting apparatuses 2 d and 2 e according to a fourth modification and a fifth modification. The first control unit 40 is omitted from the diagrams.

With the wireless power transmitting apparatus 2 d shown in FIG. 13A, an automatic tuning assist circuit 30 d is coupled in series with the transmission antenna 20 via a first transformer T1. Specifically, a secondary winding W2 of the first transformer T1 is arranged between the first terminal 31 and the second terminal 32, and a primary winding W2 of the first transformer T1 is arranged in series with the transmission antenna 20. The power supply 10 applies a driving voltage across a series circuit comprising the transmission antenna 20 and the primary winding W1. With the wireless power transmitting apparatus 2 d, energy is transmitted and received between the transmission antenna 20 and the automatic tuning assist circuit 30 d via the transformer T1. Such an arrangement provides the same advantages as those provided by the wireless power transmitting apparatuses described above.

With an arrangement shown in FIG. 13B, the power supply 10 applies the driving voltage V_(DRV) between the transmission antenna 20 side end and the automatic tuning assist circuit 30 d side end via the second transformer T2. Specifically, the second winding W2 of the second transformer T2 is arranged in series with the transmission antenna 20. The power supply 10 applies the driving voltage V_(DRV) between both ends of the primary winding W1 of the second transformer T2.

With the wireless power transmitting apparatus 2 e, the driving voltage V_(DRV) is applied between the transmission antenna 20 side end and the automatic tuning assist circuit 30 d side end via the second transformer T2. Such an arrangement also provides the same advantages as those of the wireless power transmitting apparatuses described above. With the wireless power transmitting apparatus 2 e, the first transformer T1 may be omitted. The power supply 10 shown in FIGS. 13A and 13B may be configured as an H-bridge circuit, a half-bridge circuit, or any other kind of power supply.

[Wireless Power Receiving Apparatus]

The automatic tuning assist circuit described above may also be employed in the wireless power receiving apparatus. Description will be made below regarding such a wireless power receiving apparatus.

FIG. 14 is a circuit diagram showing a configuration of a wireless power receiving apparatus 4 according to the first embodiment. The wireless power receiving apparatus 4 receives the electric power signal S1 transmitted from the aforementioned wireless power transmitting apparatus or otherwise a wireless power transmitting apparatus having an entirely different configuration. The electric power signal S1 is configured using the near-field components (electric field, magnetic field, or electromagnetic field) of electromagnetic waves that have not yet become radio waves.

The wireless power receiving apparatus 4 includes a reception antenna 50, an automatic tuning assist circuit 60, and a load 70 to be supplied with electric power. The load 70 may include an unshown rectifier circuit, detector circuit, or the like, as a built-in component.

The reception antenna 50 includes a reception coil L_(RX) and a resonance capacitor C_(RX) arranged in series between a first terminal 51 and a second terminal 52.

The automatic tuning assist circuit 60 has the same configuration as that of the automatic tuning assist circuit 30 described above. Specifically, a third switch SW3 and a third auxiliary capacitor C_(A3) are arranged between a first terminal 61 and a second terminal 62. Furthermore, a fourth switch SW4 is arranged between the first terminal 61 and the second terminal 62 such that it is connected in parallel with the third switch SW3 and the third auxiliary capacitor C_(A3).

The second control unit 64 switches on and off the third switch SW3 and the fourth switch SW4 in a complementary manner, with the same frequency as that of the electric power signal S1 and with a phase difference θ_(RX) with respect to the driving voltage (V_(DRV)) which is applied to the transmitter-side antenna. For example, the phase difference θ_(RX) is set to 180 degrees or otherwise 0 degrees.

The automatic tuning assist circuit 60 is coupled in series with the reception antenna 50. Furthermore, the load 70 to be supplied with electric power is connected to the third auxiliary capacitor C_(A3).

The above is the configuration of the wireless power receiving apparatus 4. Next, description will be made regarding the operation thereof. FIG. 15 is an equivalent circuit diagram showing an equivalent circuit configuration of the wireless power receiving apparatus 4 shown in FIG. 14. As with the automatic tuning assist circuit 30 of the wireless power transmitting apparatus 2, the automatic tuning assist circuit 60 can be regarded as a correction power supply configured to apply a correction voltage V_(A) to the reception antenna 50. During the on time T_(ON3) in which the third switch SW3 is turned on, the correction voltage V_(A) is set to the voltage V_(CA3) that develops at the third auxiliary capacitor C_(A3). During the on time T_(ON4) of the fourth switch SW4, the correction voltage V_(A) is set to the ground voltage.

FIG. 16 is a waveform diagram showing the operation of the wireless power receiving apparatus 4 shown in FIG. 14. FIG. 16 shows, in the following order beginning from the top, the voltages applied to the third switch SW3 and the fourth switch SW4, the correction voltage V_(A), the resonance current I_(RX) that flows through the reception antenna 50, and the resonance voltage V_(RX) that develops between the reception coil L_(RX) side end and the resonance capacitor C_(RX) side end. In the waveform diagrams showing the voltages applied to the respective switches, the high-level state represents the on state, and the low-level state represents the off state. In the waveform diagrams showing the resonance current I_(RX) and the resonance voltage V_(RX), the solid line represents the waveform of a steady state (quasi-resonant state) after a sufficient period of time elapses after the automatic tuning assist circuit 60 starts to operate, and the broken line represents the waveform of a non-resonant state when the automatic tuning assist circuit 60 does not operate.

By switching on and off the third switch SW3 and the fourth switch SW4 in a complementary manner, with a phase θ_(RX) which is shifted by 180 degrees or otherwise 0 degrees with respect to the driving voltage V_(DRV) of the wireless power transmitting apparatus side, such an arrangement charges or otherwise discharges the third auxiliary capacitor C_(A3). Furthermore, by applying the correction voltage V_(A) to the reception antenna 50, such an arrangement allows the resonance current I_(A) to have a phase matching the phase of the driving voltage V_(DRV) of the transmission side, thereby providing a quasi-resonant state.

In order to provide a quasi-resonant state, there is a need to switch on and off the third switch SW3 and the fourth switch SW4 with a suitable frequency f_(TX) and with a suitable phase θ_(RX). In order to meet this requirement, the wireless power transmitting apparatus 2 may be configured to transmit the data which represents the frequency f_(TX) and the phase θ_(RX) to the wireless power receiving apparatus 4. Also, the wireless power receiving apparatus 4 may be configured to sweep the phase θ_(RX) so as to detect the optimum phase θ_(RX). The above is the operation of the wireless power receiving apparatus 4.

As described above, with the wireless power receiving apparatus 4 shown in FIG. 14, such an arrangement automatically provides a resonant state without a need to adjust the capacitance of the resonance capacitor C_(RX).

Next, description will be made regarding modifications of the wireless power receiving apparatus 4.

Description has been made above regarding an arrangement in which the second control unit 64 drives the multiple switches, which are components of the automatic tuning assist circuit 60, with the same frequency as that of the electric power signal S1. However, the present invention is not restricted to such an arrangement. Also, the second control unit 64 may be configured to switch on and off the aforementioned switches with a frequency obtained by multiplying or dividing the frequency of the electric power signal S1 by an odd number. Such an arrangement also provides a quasi-resonant state.

Description has been made with reference to FIG. 14 regarding an arrangement in which the load 70 is connected to the third auxiliary capacitor C_(A3). Also, the load 70 may be connected to a different position. FIGS. 17A and 17B are circuit diagrams showing the configurations of wireless power receiving apparatuses according to a first modification and a second modification. With a wireless power receiving apparatus 4 a shown in FIG. 17A, a load 70 a is arranged in series with the reception antenna 50 and the automatic tuning assist circuit 60. Specifically, the load 70 a is connected to a first terminal 51 of the reception antenna 50.

A wireless power reception apparatus 4 b shown in FIG. 17B includes a third transformer T3 by means of which a load 70 b is insulated from the reception antenna 50. The primary winding W1 of the third transformer T3 is connected in series with the reception antenna 50. The load 70 b is connected to the secondary winding W2 of the third transformer T3.

In a case in which the load is connected in series with the reception antenna 50 as shown in FIGS. 17A and 17B, and in a case in which the load has a low impedance, such an arrangement has an advantage of a certain level of acquisition of electric power even without the adjustment by means of the automatic tuning assist circuit 60. However, such an arrangement has a disadvantage of a reduction of the Q-value of the reception antenna 50 due to the resistance component of the load. Thus, it is difficult for such an arrangement to acquire a large amount of electric power.

Conversely, in a case in which electric power is acquired from the automatic tuning assist circuit 60 as shown in FIG. 4, the Q-value of the reception antenna 50 is not reduced due to the load 70. Thus, such an arrangement is capable of acquiring a large amount of electric power even in a case in which the load 70 has a high impedance. However, in a case in which the load 70 has a very low impedance, such an arrangement has a problem of a reduction in the efficiency of the operation of the automatic tuning assist circuit 60.

Thus, the position of the load in the circuit is preferably determined giving consideration to the electric power to be transmitted, the impedance of the load, and so forth.

FIG. 18 is a circuit diagram showing a configuration of a wireless power receiving apparatus 4 c according to a third modification. An automatic tuning assist circuit 60 c further includes a fourth auxiliary capacitor C_(A4) between the first terminal 61 and the second terminal 62 such that it is connected in series with the fourth switch SW4. The position of the load 70 is not restricted in particular.

With such a modification, during the on time T_(ON3) of the third switch SW3, the correction voltage V_(A) is set to the capacitor voltage V_(CA3), and during the on time T_(ON4) of the fourth switch SW4, the correction voltage V_(A) is set to the capacitor voltage V_(CA4). With the wireless power receiving apparatus 4 c, the capacitor voltages V_(CA1) and V_(CA2) can be optimized so as to provide a quasi-resonant state in both the state in which f_(TX)>f_(c) and the state in which f_(TX)<f_(c).

With such a wireless power receiving apparatus, the third switch SW3 and the fourth switch SW4 may each be configured as a uni-directional switch or otherwise a bi-directional switch. In a case in which the third switch SW3 and the fourth switch SW4 are each configured as a uni-directional switch, there is a need to switch on and off the third switch SW3 and the fourth switch SW4 with a phase such that no current flows through each of the inversely conducting elements.

FIGS. 19A and 19B are circuit diagrams showing the configurations of wireless power receiving apparatuses according to a fourth modification and a fifth modification, respectively. The second control unit 64 is omitted from the diagrams.

With a wireless power receiving apparatus 4 d shown in FIG. 19A, an automatic tuning assist circuit 60 d is coupled in series with the reception antenna 50 via a fourth transformer T4. Specifically, the secondary winding W2 of the fourth transformer T4 is arranged between the first terminal 61 and the second terminal 62. The primary winding W1 of the fourth transformer T4 is arranged in series with the reception antenna 50.

With the wireless power receiving apparatus 4 d, energy is transmitted and received between the reception antenna 50 and the automatic tuning assist circuit 60 d via the fourth transformer T4. Such an arrangement provides the same advantages as those provided by the wireless power receiving apparatuses described above.

FIG. 19B shows an arrangement in which the load 70 is coupled with the reception antenna 50 and the automatic tuning assist circuit 60 d via a fifth transformer T5. Specifically, the primary winding W1 of the fifth transformer T5 is connected in series with the reception antenna 50. The load 70 is connected between both ends of the secondary winding W2 of the fifth transformer T5.

Such an arrangement also provides the same advantages as those provided by the wireless power receiving apparatuses described above. With such a wireless power receiving apparatus 4 e, the fourth transformer T4 may be omitted. With such an arrangement shown in FIG. 19A, the load 70 may be coupled with the third auxiliary capacitor C_(A3). Also, with such an arrangement shown in FIG. 19B, the load 70 may be coupled with the third capacitor C_(A3) via a fifth transformer T5.

[Wireless Power Transmission System]

By combining the wireless power transmitting apparatus and the wireless power receiving apparatus described above, such an arrangement provides a wireless power transmission system.

FIG. 20 is a circuit diagram showing an example configuration of a wireless power transmission system according to the first embodiment. The wireless power transmission system 1 includes the wireless power transmitting apparatus 2 and the wireless power receiving apparatus 4.

The load 70 includes a rectifier circuit 72 and a switching regulator 74, in addition to a load circuit 76. The rectifier circuit 72 is configured as a synchronous detector circuit, and includes a smoothing capacitor C3, a third high-side switch SWH3, and a third low-side switch SWL3. The switching regulator 74 is configured as a step-up converter, and controlled so as to be capable of supplying the load circuit 76 with the maximum electric power. The configuration and the operation of the switching regulator 74 are known, and accordingly, description thereof will be omitted.

The above is the configuration of the wireless power transmission system 1. FIG. 21 is a waveform diagram showing the operation of the wireless power transmission system 1 shown in FIG. 20.

With the wireless power transmitting apparatus 2, the first switch SW1 and the second switch SW2 are driven with a phase that is delayed by θ_(TX)=90 degrees with respect to the driving voltage V_(DRV). As a result, the wireless power transmitting apparatus 2 provides a quasi-resonant state.

With the wireless power receiving apparatus 4, the third switch SW3 and the fourth switch SW4 are driven with a phase that is delayed by θ_(RX)=180 degrees with respect to the driving voltage V_(DRV) employed on the wireless power transmitting apparatus 2 side. The third switch SW3 is driven with a phase that is delayed by 90 degrees with respect to the first switch SW1. As a result, the wireless power receiving apparatus 4 also provides a quasi-resonant state.

The third high-side switch SWH3 and the third low-side switch SWL3 of the rectifier circuit 72 are driven with a phase that is delayed by 90 degrees with respect to the third switch SW3 and the fourth switch SW4. As a result, a DC voltage is generated at the smoothing capacitor C3. The switching regulator 74 converts the DC voltage thus generated into an optimum voltage level for the load circuit 76.

The above is the operation of the wireless power transmission system 1. As described above, with the wireless power transmission system 1, the wireless power transmitting apparatus 2 and the wireless power receiving apparatus 4 each include an automatic tuning assist circuit. Thus, such an arrangement allows the maximum electric power to be transmitted to the load 70.

It is needless to say that any of the aforementioned wireless power transmitting apparatuses 2 including the modifications may be combined with any of the aforementioned wireless power receiving apparatuses 4 including the modifications.

Description has been made with reference to FIG. 20 regarding an arrangement in which an automatic tuning assist circuit is mounted on both the wireless power transmitting apparatus 2 and the wireless power receiving apparatus 4. However, the present invention is not restricted to such an arrangement.

Also, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power transmitting apparatus 2, and the wireless power receiving apparatus adjusts the resonance capacitor C_(RX) in the same way as with conventional techniques.

Conversely, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power receiving apparatus 4, and the wireless power transmitting apparatus 2 adjusts the resonance capacitor C_(TX) in the same way as with conventional techniques.

Also, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power transmitting apparatus 2, and the wireless power receiving apparatus 4 has no adjustment mechanism. Alternatively, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power receiving apparatus 4, and the wireless power transmitting apparatus 2 has no adjustment mechanism.

With such arrangements, tuning is performed by means of a single automatic tuning assist circuit so as to provide impedance matching between the power supply 10 and the load 70, thereby providing high-efficiency electric power transmission. It is needless to say that, with such arrangements, the optimum value of the phase θ_(TX) (θ_(RX)) of the switching of the automatic tuning assist circuit does not match the aforementioned values, i.e., 90 degrees or otherwise 270 degrees (180 degrees or otherwise 0 degrees).

Description has been made regarding the present invention with reference to the first embodiment. The above-described embodiment has been described for exemplary purposes only, and is by no means intended to be interpreted restrictively. Rather, it can be readily conceived by those skilled in this art that various modifications may be made by making various combinations of the aforementioned components or processes, which are also encompassed in the technical scope of the present invention. Description will be made below regarding such modifications.

With the wireless power transmitting apparatus 2 including the automatic tuning assist circuit 30, in some cases, such an arrangement is capable of providing a quasi-resonant state even without including the resonance capacitor C_(TX). In this case, such a resonance capacitor C_(TX) may be omitted. In the same way, an arrangement may be made in which the wireless power receiving apparatus 4 including the automatic tuning assist circuit 60 does not include the resonance capacitor C_(RX).

The wireless power transmitting apparatus 2 encrypts the electric power signal S1 by changing at least one of the frequency f_(TX) and the phase of the driving voltage V_(DRV) according to a predetermined rule (encryption code). In a case in which the wireless power receiving apparatus 4 knows the encryption code, the wireless power receiving apparatus 4 controls the switching frequency and phase of the automatic tuning assist circuit 60 based on the encryption code. As a result, even if the electric power signal S1 is encrypted, such an arrangement is capable of decrypting the electric power signal S1 and receiving the power supply. In a case in which a wireless power receiving apparatus does not know the encryption code, the wireless power receiving apparatus cannot appropriately control the switching operation of the automatic tuning assist circuit 60. Thus, such a wireless power receiving apparatus cannot receive electric power. With wireless power transmission, there is a problem of potential power theft by malicious users. However, by employing such an automatic tuning assist circuit, such a problem can be solved.

Also, in a case in which a single wireless power transmitting apparatus 2 supplies electric power to multiple wireless power receiving apparatuses 4, by employing such an automatic tuning assist circuit, such an arrangement is capable of controlling the amount of electric power to be supplied to each terminal.

Second Embodiment

Description has been made in the first embodiment regarding the automatic tuning assist circuit including the two switches SW1 and SW2. An automatic tuning assist circuit according to a second embodiment has a configuration including four switches. The automatic tuning assist circuit according to the second embodiment has the same block configuration as that of the first embodiment except for the automatic tuning assist circuit 80. Also, various kinds of modifications as described in the first embodiment may effectively be made for the second embodiment.

[Wireless Power Receiving Apparatus]

FIG. 22 is a circuit diagram showing a configuration of a wireless power transmitting apparatus 2 according to a second embodiment. The wireless power transmitting apparatus 2 transmits an electric power signal S1 to a wireless power receiving apparatus (not shown). The electric power signal S1 is configured using the near-field components (electric field, magnetic field, or electromagnetic field) of electromagnetic waves that have not yet become radio waves. The wireless power transmitting apparatus 6 includes a power supply 10, a transmission antenna 20, an automatic tuning assist circuit 80, and a first control unit 40.

The transmission antenna 20 includes a transmission coil L_(TX) arranged between its first terminal 21 and its second terminal 22. A resonance capacitor C_(TX) is arranged in series with the transmission coil L_(TX). The resonance capacitor C_(TX) and the transmission coil L_(TX) may also be mutually exchanged.

The automatic tuning assist circuit 80 is coupled in series with the transmission antenna 20. The power supply 10 is configured as a half-bridge circuit in the same way as shown in FIG. 2. The power supply 10 applies an AC driving voltage V_(DRV) having a predetermined transmission frequency f_(TX) across a series circuit that comprises the transmission antenna 20 and the automatic tuning assist circuit 80. The driving voltage V_(DRV) may be configured to have a desired AC waveform, examples of which include a rectangular waveform, a trapezoidal waveform, a sine waveform, and the like. With the present embodiment, the driving voltage V_(DRV) is configured as a rectangular wave signal which swings between a first voltage level (power supply voltage V_(DD)) and a second voltage level (ground voltage V_(GND)=0 V).

The power supply 10 is configured as a half-bridge circuit, as with the power supply 10 shown in FIG. 2. The first control unit 40 switches on and off the first high-side switch SWH1 and the first low-side switch SWL1 in a complementary manner, with a transmission frequency f_(TX).

With the second embodiment, the automatic tuning assist circuit 80 includes a first terminal 81, a second terminal 82, a first switch SWc1 through a fourth switch SWc4, and a first auxiliary capacitor C_(A5).

The first switch SWc1 and the second switch SWc2 are sequentially arranged in series between the first terminal 81 and the second terminal 82. The third switch SWc3 and the fourth switch SWc4 are sequentially arranged between the first terminal 81 and the second terminal 82, and are arranged in parallel with the first switch SWc1 and the second switch SWc2. The first auxiliary capacitor C_(A5) is arranged between a connection node N1 that connects the first switch SWc1 and the second switch SWc2 and a connection node N2 that connects the third switch SWc3 and the fourth switch SWc4. The first auxiliary capacitor C_(A5) is preferably configured to have a capacitance that is sufficiently greater than that of the resonance capacitor C_(TX).

The first control unit 40 switches on and off the first switch SWc1 through the fourth switch SWc4 in a complementary manner, with the same frequency f_(TX) as that of the driving voltage V_(DRV), and with a predetermined phase difference θ_(TX) with respect to the driving voltage V_(DRV). The phase difference θ_(TX) is preferably set to a value in the vicinity of +90 degrees or otherwise −90 degrees (270 degrees). That is to say, a part of the first control unit 40 functions as a component of the automatic tuning assist circuit 80.

In the same way as with the first embodiment, the first switch SWc1 through the fourth switch SWc4 may each be configured as a uni-directional switch or otherwise a bi-directional switch. In a case in which the first switch SWc1 through the fourth switch SWc4 are each configured as a uni-directional switch, there is a need to pay attention to their switching phases, as described above in the first embodiment. The above is the configuration of the wireless power transmitting apparatus 6. Next, description will be made regarding the operation thereof.

FIG. 23 is a waveform diagram showing the operation of the wireless power transmitting apparatus 6 shown in FIG. 22. FIG. 23 shows, in the following order beginning from the top, the voltage at the first high-side switch SWH1, the voltage at the first low-side switch SWL1, the driving voltage V_(DRV), the voltage at the first switch SWc1, the voltage at the second switch SWc2, the voltage at the third switch SWc3, the voltage at the fourth switch SWc4, the correction voltage V_(A) generated at the first terminal 81, the resonance current I_(TX) that flows through the transmission antenna 20, and the resonance voltage V_(TX) that develops between the transmission coil L_(TX) side end and the resonance capacitor C_(TX) side end. In the waveform diagram for each switch, the high level represents the on state, and the low level represents the off state. It should be noted that FIG. 23 shows the waveforms of the resonance current I_(TX) and the resonance voltage V_(TX) obtained after a sufficient time has elapsed after the automatic tuning assist circuit 80 starts to operate.

As shown in FIG. 23, by switching on and off the first high-side switch SWH1 and the first low-side switch SWL1 in a complementary manner, such an arrangement is capable of generating the driving voltage V_(DRV) having a rectangular waveform. The driving voltage V_(DRV) thus generated is applied between the transmission antenna 20 side end and the automatic tuning assist circuit 80 side end. The first control unit 40 drives a first pair P1 comprising the first switch SWc1 and the fourth switch SWc4 with the same frequency as that of the driving voltage V_(DRV), and with a phase that is delayed by θ_(TX) (=90 degrees) with respect to the driving voltage V_(DRV). Furthermore, the first control unit 40 drives a second pair P2 comprising the second switch SWc2 and the third switch SWc3 in a complementary manner with respect to the first pair P1, i.e., with a phase that is shifted by 180 degrees with respect to that of the first pair P1.

During the on time T_(ON1) of the first pair P1, the resonance current I_(TX) flows through a path including the first switch SWc1, the first auxiliary capacitor C_(A5), and the fourth switch SWc4. During the on time T_(ON2) of the second pair P2, the resonance current I_(TX) flows through a path including the third switch SWc3, the first auxiliary capacitor C_(A5), and the second switch SWc2.

That is to say, the first auxiliary capacitor C_(A5) is charged and discharged by means of the resonance current I_(TX). As a result, the capacitor voltage V_(CA5) develops at the first auxiliary capacitor C_(A5).

The automatic tuning assist circuit 80 applies a correction voltage V_(A) to the second terminal 22 of the transmission antenna 20. During the on time T_(ON1) of the first pair P1, the correction voltage V_(A) is set to a first polarity. During the on time T_(ON2) of the second pair P2, the correction voltage V_(A) is set to a second polarity. The automatic tuning assist circuit 80 can be regarded as a correction power supply configured to apply the correction voltage V_(A) to the transmission antenna 20. That is to say, it can be clearly understood that the wireless power transmitting apparatus 6 can be represented by the same equivalent circuit as that shown in FIG. 5, and is configured to operate according to the same operation mechanism.

That is to say, in a case in which the automatic tuning assist circuit 80 operates, the correction voltage V_(A) is applied to the transmission antenna 20 with a phase that is delayed by θ_(TX)=90 degrees with respect to the driving voltage V_(DRV). As a result, phase matching is obtained between the resonance current I_(TX) and the driving voltage V_(DRV), thereby providing a quasi-resonant state. In this state, the resonance current I_(TX) has a greater amplitude than that in the non-resonant state. This is as shown in the phasor diagrams in FIGS. 7 and 9.

The operation of the automatic tuning assist circuit 80 according to the second embodiment is the same as described in the first embodiment with reference to FIG. 8. Thus, such an arrangement is capable of automatically generating the correction voltage V_(A) which provides a quasi-resonant state.

The above is the operation of the wireless power transmitting apparatus 6.

As described above, without adjusting the resonance frequency f_(c) of the transmission antenna 20, the wireless power transmitting apparatus 6 is capable of automatically tuning the circuit state so as to provide the quasi-resonant state. In the wireless power transmission, the resonance frequency changes over time according to the position relation between the wireless power transmitting apparatus and the wireless power receiving apparatus. The wireless power transmitting apparatus 6 is capable of following the change in the resonance frequency with high speed, thereby providing high-efficiency electric power transmission.

Furthermore, in a case in which a large amount of electric power is transmitted by means of wireless power transmission, a very high voltage develops between both ends of the resonance capacitor C_(TX), which limits the use of a variable capacitor. With the wireless power transmitting apparatus 6, there is no need to adjust the capacitance of the resonance capacitor C_(TX). Thus, such an arrangement does not require such a variable capacitor or the like, which is another advantage.

Description has been made above regarding an arrangement in which the first pair comprising the first switch SWc1 and the fourth switch SWc4 is switched on and off with a phase that is delayed by θ_(TX) (=90 degrees) with respect to the phase of the switching of the first high-side switch SWH1 (driving voltage V_(DRV)). However, the phase difference θ_(TX) between the first pair and the first high-side switch SWH1 is not restricted to 90 degrees. Also, an arrangement may be made in which the phase difference θ_(TX) between the first pair and the first high-side switch SWH1 is set to 270 degrees (−90 degrees). In this case, the capacitor voltage V_(CA1) is automatically adjusted such that the polarity reverses. In a case in which the first switch SWc1 through the fourth switch SWc4 are each configured as a uni-directional switch, there is a need to switch on and off the first switch SWc1 through the fourth switch SWc4 with a phase such that no current flows through each of the inversely conducting elements. Specifically, in a case in which f_(c)<f_(TX), the phase difference θ_(TX) is preferably set to 90 degrees. Conversely, in a case in which f_(c)>f_(TX), the phase difference θ_(TX) is preferably set to 270 degrees.

Also, the phase difference θ_(TX) may be moved away from 90 degrees or 270 degrees, as described in the first embodiment.

Next, description will be made regarding modifications of the wireless power transmitting apparatus 6. Each modification may be combined with any one of the other modifications, which is encompassed within the scope of the present invention.

Description has been made above regarding an arrangement in which the first control unit 40 drives multiple switches included in the automatic tuning assist circuit 80 with the same frequency f_(TX) as that of the driving voltage V_(DRV). However, the present invention is not restricted to such an arrangement. Also, the first control unit 40 may be configured to switch on and off the aforementioned switches with a frequency obtained by multiplying or dividing the frequency of the driving voltage V_(DRV) by an odd number. Such an arrangement also provides a quasi-resonant state.

FIG. 24 is a circuit diagram showing a configuration of a wireless power transmitting apparatus 6 a according to a first modification. A power supply 10 c shown in FIG. 24 is configured as an H-bridge circuit. A transmission antenna 20 and an automatic tuning assist circuit 80 a are arranged in series between a first output terminal OUT1 and a second output terminal OUT2 of a power supply 10 c. Furthermore, a capacitor C2 configured to block DC current is arranged in series with the transmission antenna 20 and the automatic tuning assist circuit 80 a. With the automatic tuning assist circuit 80 a, one end (N2) of a first auxiliary capacitor C_(A5) is grounded.

With the wireless power transmitting apparatus 6 a shown in FIG. 24, such an arrangement provides the same advantages as those provided by the wireless power transmitting apparatuses described above.

As described in the first embodiment, the power supply, the automatic tuning assist circuit, or otherwise both of them, may be coupled with the transmission antenna 20 via a transformer. FIGS. 25A through 25C are circuit diagrams respectively showing the configurations of wireless power transmitting apparatuses 6 b through 6 d according to second through fourth modifications. The first control unit 40 is not shown.

With the wireless power transmitting apparatus 6 b shown in FIG. 25A, the automatic tuning assist circuit 80 a is coupled in series with the transmission antenna 20 via a sixth transformer T6. Specifically, the sixth transformer T6 is configured to have a primary winding W1 connected in series with the transmission antenna 20, and to have a secondary winding W2 connected between the first terminal 61 and the second terminal 62 of the automatic tuning assist circuit 80 a. The power supply 10 c applies a driving voltage across a series circuit that comprises the transmission antenna 20 and the primary winding W1 of the sixth transformer T6.

With a wireless power transmitting apparatus 6 c shown in FIG. 25B, the power supply 10 c is coupled with the transmission antenna 20 and the automatic tuning assist circuit 80 a via a seventh transformer T7. The power supply 10 c applies a driving voltage across the primary winding W1 of the seventh transformer T7. The transmission antenna 20 and the automatic tuning assist circuit 80 a are arranged in series with the secondary winding W2.

With a wireless power transmitting apparatus 6 d shown in FIG. 25C, the power supply 10 having a half-bridge configuration is coupled with the transmission antenna 20 and the automatic tuning assist circuit 80 a via the seventh transformer T7. A capacitor C3 configured to block DC current is arranged between the output terminal of the power supply 10 and the first winding W1 of the seventh transformer T7.

Also, the modifications shown in FIGS. 25A through 25C may be combined. That is to say, both the power supply and the automatic tuning assist circuit may be coupled with the transmission antenna via a transformer.

Such modifications also provide the same advantages provided by the wireless power transmitting apparatuses described above.

[Wireless Power Receiving Apparatus]

The automatic tuning assist circuit according to the second embodiment described above may be employed in a wireless power receiving apparatus. Description will be made below regarding such a wireless power receiving apparatus.

FIG. 26 is a circuit diagram showing a wireless power receiving apparatus 8 according to the second embodiment. The wireless power receiving apparatus 8 receives the electric power signal S1 transmitted from the aforementioned wireless power transmitting apparatus or otherwise a wireless power transmitting apparatus having an entirely different configuration. The electric power signal S1 is configured using the near-field components (electric field, magnetic field, or electromagnetic field) of electromagnetic waves that have not yet become radio waves.

The wireless power receiving apparatus 8 includes a reception antenna 50, an automatic tuning assist circuit 90, and a load 70 to be supplied with electric power. The load 70 may include an unshown rectifier circuit, detector circuit, or the like, as a built-in component.

The reception antenna 50 includes a reception coil L_(RX) and a resonance capacitor C_(RX) arranged in series between a first terminal 51 and a second terminal 52.

The automatic tuning assist circuit 90 has the same configuration as that of the automatic tuning assist circuit 80 shown in FIG. 22. Specifically, the automatic tuning assist circuit 90 includes a first terminal 91, a fifth switch SWc5 through an eighth switch SWc8, and a second auxiliary capacitor C_(A6).

The fifth switch SWc5 and the sixth switch SWc6 are arranged in series between the first terminal 91 and the second terminal 92. The seventh switch SWc7 and the eighth switch SWc8 are sequentially arranged in series between the first terminal 91 and the second terminal 92. Furthermore, the seventh switch SWc7 and the eighth switch SWc8 are arranged in parallel with the fifth switch SWc5 and the sixth switch SWc6. The second auxiliary capacitor C_(A6) is arranged between a connection node N3 that connects the fifth switch SWc5 and the sixth switch SWc6 and a connection node N4 that connects the seventh switch SWc7 and the eighth switch SWc8. The second auxiliary capacitor C_(A6) is preferably configured to have a sufficiently great capacitance as compared with the resonance capacitance C_(RX).

A second control unit 94 is configured to switch on and off the fifth switch SWc5 through the eighth switch SWc8 with the same frequency as that of the electric power signal S1, and with a phase difference θ_(RX) with respect to the driving voltage (V_(DRV)) which is applied to the transmitter-side antenna. For example, the phase difference θ_(RX) is preferably set to 180 degrees or otherwise 0 degrees.

The automatic tuning assist circuit 90 is coupled in series with the reception antenna 50. Furthermore, the load 70 to be supplied with electric power is directly connected with the reception antenna 50 and the automatic tuning assist circuit 90.

The above is the configuration of the wireless power receiving apparatus 8. Next, description will be made regarding the operation thereof. The wireless power receiving apparatus 8 can be represented by the same equivalent circuit diagram as that which represents the wireless power receiving apparatus 4 shown in FIG. 15. As with the automatic tuning assist circuit 80 of the wireless power transmitting apparatus 6, the automatic tuning assist circuit 90 can be regarded as a correction power supply configured to apply a correction voltage V_(A) to the reception antenna 50.

FIG. 27 is a waveform diagram showing the operation of the wireless power receiving apparatus 8 shown in FIG. 26. FIG. 27 shows the voltages applied to the fifth switch SWc5 through the eighth switch SWc8, the correction voltage V_(A), the resonance current I_(RX) that flows through the reception antenna 50, and the resonance voltage V_(RX) that develops between the reception coil L_(RX) side end and the resonance capacitor C_(RX) side end. In the waveform diagrams showing the voltages applied to the respective switches, the high-level state represents the on state, and the low-level state represents the off state.

A first pair comprising the fifth switch SWc5 and the eighth switch SWc8 is switched on and off with a phase θ_(RX) which is shifted by 180 degrees or otherwise 0 degrees with respect to the driving voltage V_(DRV) of the wireless power transmitting apparatus side. A second pair comprising the sixth switch SWc6 and the seventh switch SWc7 is switched on and off in a complementary manner with respect to the first pair. During the on time T_(ON1) of the first pair, the resonance current I_(RX) flows through a path comprising the fifth switch SWc5, the second auxiliary capacitor C_(A6), and the eighth switch SWc8. During the on time T_(ON2) of the second pair, the resonance current I_(RX) flows through a path comprising the sixth switch SWc6, the second auxiliary capacitor C_(A6), and the seventh switch SWc7.

The second auxiliary capacitor C_(A6) is charged and discharged by means of the resonance current I_(RX). As a result, a capacitor voltage V_(CA6) develops at the capacitor C_(A6). With such an arrangement, the correction voltage V_(A) that corresponds to the capacitor voltage V_(CA6) is applied to the reception antenna 50. Thus, such an arrangement allows the resonance current I_(A) to have a phase that matches the phase of the driving voltage V_(DRV) that is used in the transmitter side, thereby providing a quasi-resonant state.

In order to provide a quasi-resonant state, there is a need to switch on and off the fifth switch SWc5 and the eighth switch SWc8 with a suitable frequency f_(TX) and with a suitable phase θ_(RX). In order to meet this requirement, the wireless power transmitting apparatus may be configured to transmit the data which represents the frequency f_(TX) and the phase θ_(RX) to the wireless power receiving apparatus 8. Also, the wireless power receiving apparatus 8 may be configured to sweep the phase θ_(RX) so as to detect the optimum phase θ_(RX).

The above is the operation of the wireless power receiving apparatus 8.

As described above, with the wireless power receiving apparatus 8 shown in FIG. 26, such an arrangement automatically provides a resonant state without a need to adjust the capacitance of the resonance capacitor C_(RX).

Next, description will be made regarding modifications of the wireless power receiving apparatus 8.

Description has been made above regarding an arrangement in which the second control unit 64 drives the multiple switches, which are components of the automatic tuning assist circuit 30, with the same frequency as that of the electric power signal S1. However, the present invention is not restricted to such an arrangement. Also, the second control unit 64 may be configured to switch on and off the aforementioned switches with a frequency obtained by multiplying or dividing the frequency of the electric power signal S1 by an odd number. Such an arrangement also provides a quasi-resonant state.

Description has been made with reference to FIG. 26 regarding an arrangement in which one terminal of the load 70 is grounded, and the ground potential is used as the reference potential. Also, instead of such an arrangement in which one terminal of the load 70 is grounded, one terminal of the second auxiliary capacitor C_(A6) of the automatic tuning assist circuit 90, i.e., either the connection node N3 or N4, may be grounded.

FIGS. 28A and 28B are circuit diagrams showing the configurations of wireless power receiving apparatuses according to a second modification and a third modification.

Description has been made with reference to FIG. 26 regarding an arrangement in which the load 70 is connected in series with the reception antenna 50. Also, the load 70 may be arranged at a different position.

With a wireless power receiving apparatus 8 a according to a first modification shown in FIG. 28A, the connection node N4 of the automatic tuning assist circuit 90 a is grounded. A load 70 a is arranged in parallel with the second auxiliary capacitor C_(A6). That is to say, the load 70 a is supplied with a capacitor voltage V_(CA6) that develops at the second auxiliary capacitor C_(A6).

With a wireless power receiving apparatus 8 b according to a second modification shown in FIG. 28B, a load 70 b is coupled via an eighth transformer T8 with a series circuit comprising the reception antenna 50 and the automatic tuning assist circuit 90 a.

FIGS. 28C and 28D are circuit diagrams each showing an example configuration of such a load. A load 70 c shown in FIG. 28C includes a diode rectifier circuit 72 c and a load circuit 76. A load 70 d shown in FIG. 28D includes a synchronous detector circuit 72 d and the load circuit 76. Such a load circuit may further include a switching regulator 74 as shown in FIG. 20.

Such an automatic tuning assist circuit 90 may be coupled in series with the reception antenna 50 via a transformer. FIG. 29 is a circuit diagram showing a configuration of a wireless power receiving apparatus 8 c according to a third modification. The automatic tuning assist circuit 90 a is coupled in series with the reception antenna 50 via a ninth transformer T9. A load may be arranged in series with the reception antenna 50 and the primary winding W1. Also, such a load may be arranged in parallel with the second auxiliary capacitor C_(A6).

Such modifications also provide the same advantages as those provided by the wireless power receiving apparatus 8 shown in FIG. 26.

In a case in which the load is connected in series with the reception antenna 50 as shown in FIG. 26, and in a case in which the load has a low impedance, such an arrangement has an advantage of a certain level of acquisition of electric power even without the adjustment by means of the automatic tuning assist circuit 90. However, such an arrangement has a disadvantage of a reduction of the Q-value of the reception antenna 50 due to the resistance component of the load. Thus, it is difficult for such an arrangement to acquire a large amount of electric power.

Conversely, in a case in which electric power is acquired from the automatic tuning assist circuit 90 a as shown in FIG. 28A, the Q-value of the reception antenna 50 is not reduced due to the load 70. Thus, such an arrangement is capable of acquiring a large amount of electric power even in a case in which the load 70 a has a high impedance. However, in a case in which the load 70 a has a very low impedance, such an arrangement has a problem of a reduction in the efficiency of the operation of the automatic tuning assist circuit 60.

Thus, the position of the load in the circuit is preferably determined giving consideration to the electric power to be transmitted, the impedance of the load, and so forth.

The fifth switch SWc5 through the eighth switch SWc8 may each be configured as a uni-directional switch or otherwise a bi-directional switch. As described above, in a case in which these switches are each configured as a uni-directional switch, there is a need to pay attention to their switching phases.

[Wireless Power Transmission System]

By combining the wireless power transmitting apparatus 6 and the wireless power receiving apparatus 8 described in the second embodiment, such an arrangement provides a wireless power transmission system.

Description has been made regarding an arrangement in which an automatic tuning assist circuit is mounted on each of the wireless power transmitting apparatus 6 and the wireless power receiving apparatus 8. However, the present invention is not restricted to such an arrangement.

Also, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power transmitting apparatus 6, and the wireless power receiving apparatus adjusts the resonance capacitor C_(RX) in the same way as with conventional techniques. Conversely, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power receiving apparatus 8, and the wireless power transmitting apparatus 6 adjusts the resonance capacitor C_(TX) in the same way as with conventional techniques.

Also, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power transmitting apparatus 6, and the wireless power receiving apparatus 8 has no adjustment mechanism. Alternatively, an arrangement may be made in which such an automatic tuning assist circuit is provided to only the wireless power receiving apparatus 8, and the wireless power transmitting apparatus 6 has no adjustment mechanism.

With such arrangements, tuning is performed by means of a single automatic tuning assist circuit so as to provide impedance matching between the power supply 10 and the load 70, thereby providing high-efficiency electric power transmission. It should be noted that, with such arrangements, the optimum value of the phase θ_(TX) (θ_(RX)) of the switching of the automatic tuning assist circuit does not match the aforementioned values, i.e., 90 degrees or otherwise 270 degrees (180 degrees or otherwise 0 degrees).

Also, the wireless power transmitting apparatus 2 according to the first embodiment may be combined with the wireless power receiving apparatus 8 according to the second embodiment. Also, the wireless power receiving apparatus 4 according to the first embodiment may be combined with the wireless power transmitting apparatus 6 according to the second embodiment.

Description has been made regarding the present invention with reference to the second embodiment. The above-described embodiment has been described for exemplary purposes only, and is by no means intended to be interpreted restrictively. Rather, it can be readily conceived by those skilled in this art that various modifications may be made by making various combinations of the aforementioned components or processes, which are also encompassed in the technical scope of the present invention. Description will be made below regarding such modifications.

With the wireless power transmitting apparatus 6 including the automatic tuning assist circuit 80, in some cases, such an arrangement is capable of providing a quasi-resonant state even while omitting the resonance capacitor C_(TX). In this case, such a resonance capacitor C_(TX) may be omitted. In the same way, an arrangement may be made in which the wireless power receiving apparatus 8 including the automatic tuning assist circuit 90 does not include the resonance capacitor C_(RX).

The wireless power transmitting apparatus 6 encrypts the electric power signal S1 by changing at least one of the frequency f_(TX) and the phase of the driving voltage V_(DRV) according to a predetermined rule (encryption code). In a case in which the wireless power receiving apparatus 8 knows the encryption code, the wireless power receiving apparatus 8 controls the switching frequency and phase of the automatic tuning assist circuit 90 based on the encryption code. As a result, even if the electric power signal S1 is encrypted, such an arrangement is capable of decrypting the electric power signal S1 and receiving the power supply. In a case in which the wireless power receiving apparatus does not know the encryption code, the wireless power receiving apparatus cannot appropriately control the switching operation of the automatic tuning assist circuit 90. Thus, such a wireless power receiving apparatus cannot receive electric power. With wireless power transmission, there is a problem of potential power theft by malicious users. However, by employing such an automatic tuning assist circuit, such a problem can be solved.

Also, in a case in which a single wireless power transmitting apparatus 6 supplies electric power to multiple wireless power receiving apparatuses 8, by employing such an automatic tuning assist circuit, such an arrangement is capable of controlling the amount of electric power to be supplied to each terminal.

The usage of the automatic tuning assist circuit 30 is not restricted to such wireless power transmission. Rather, the present invention is applicable to various kinds of applications which require tuning.

While the preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the appended claims. 

What is claimed is:
 1. A wireless power transmitting apparatus configured to transmit an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field to a wireless power receiving apparatus, the wireless power transmitting apparatus comprising: a transmission antenna comprising a transmission coil; an automatic tuning assist circuit coupled with the transmission antenna; and a power supply configured to apply an AC driving voltage across a series circuit that comprises the transmission antenna and the automatic tuning assist circuit, wherein the automatic tuning assist circuit comprises: a first terminal; a second terminal; a first switch and a second switch arranged in series between the first terminal and the second terminal; a third switch and a fourth switch sequentially arranged in series between the first terminal and the second terminal such that they are arranged on a path that is in parallel with the first switch and the second switch; a first auxiliary capacitor arranged between a connection node that connects the first switch and the second switch and a connection node that connects the third switch and the fourth switch; and a first control unit configured to switch on and off the first switch through the fourth switch in synchronization with the driving voltage.
 2. The wireless power transmitting apparatus according to claim 1, wherein the first control unit is configured to switch on and off each of the first switch through the fourth switch with the same frequency as that of the driving voltage, or otherwise with a frequency obtained by multiplying or dividing the frequency of the driving voltage by an odd number.
 3. The wireless power transmitting apparatus according to claim 1, wherein the power supply comprises: a DC power supply; and a first high-side switch and a first low-side switch sequentially arranged in series between an output terminal of the DC power supply and a fixed voltage terminal, and wherein the transmission antenna and the automatic tuning assist circuit are coupled in series between a connection node that connects the first high-side switch and the first low-side switch and the fixed voltage terminal.
 4. The wireless power transmitting apparatus according to claim 1, wherein the power supply comprises: a DC power supply; a first high-side switch and a first low-side switch sequentially arranged in series between an output terminal of the DC power supply and a fixed voltage terminal; and a second high-side switch and a second low-side switch sequentially arranged in series between the output terminal of the DC power supply and the fixed voltage terminal, and wherein the transmission antenna and the automatic tuning assist circuit are coupled in series between a connection node that connects the first high-side switch and the first low-side switch and a connection node that connects the second high-side switch and the second low-side switch.
 5. The wireless power transmitting apparatus according to claim 1, wherein the first switch through the fourth switch are each configured as a uni-directional switch, and wherein the first control unit is configured to switch on and off the first switch through the fourth switch with a phase controlled such that no current flows through each of their inversely conducting elements.
 6. The wireless power transmitting apparatus according to claim 1, wherein the first switch through the fourth switch are each configured as a bi-directional switch.
 7. The wireless power transmitting apparatus according claim 1, wherein the automatic tuning assist circuit is coupled in series with the transmission antenna via a transformer.
 8. The wireless power transmitting apparatus according to claim 1, wherein the transmission antenna comprises a resonance capacitor arranged in series with the transmission coil.
 9. The wireless power transmitting apparatus according to claim 1, wherein the power supply is configured to apply an AC driving voltage via a transformer across a series circuit that comprises the transmission antenna and the automatic tuning assist circuit.
 10. A wireless power supply system comprising: the wireless power transmitting apparatus according to claim 1; and a wireless power receiving apparatus configured to receive an electric power signal from the wireless power transmitting apparatus.
 11. A wireless power receiving apparatus configured to receive an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field, transmitted from a wireless power transmitting apparatus, the wireless power receiving apparatus comprising: a reception antenna comprising a reception coil; and an automatic tuning assist circuit coupled with the reception antenna; wherein the automatic tuning assist circuit comprises: a first terminal; a second terminal; a fifth switch and a sixth switch arranged in series between the first terminal and the second terminal; a seventh switch and an eighth switch sequentially arranged in series between the first terminal and the second terminal such that they are arranged in parallel with the fifth switch and the sixth switch; a second auxiliary capacitor arranged between a connection node that connects the fifth switch and the sixth switch and a connection node that connects the seventh switch and the eighth switch; and a second control unit configured to switch on and off the fifth switch through the eighth switch.
 12. The wireless power receiving apparatus according to claim 11, wherein the second control unit is configured to switch on and off each of the fifth switch through the eighth switch with the same frequency as that of the electric power signal, or otherwise with a frequency obtained by multiplying or dividing the frequency of the electric power signal by an odd number.
 13. The wireless power receiving apparatus according to claim 11, wherein a load to which electric power is to be supplied is connected to the second auxiliary capacitor.
 14. The wireless power receiving apparatus according to claim 11, wherein a load to which electric power is to be supplied is connected to the reception antenna.
 15. The wireless power receiving apparatus according to claim 11, further comprising a transformer having a primary winding connected in series with the reception antenna, wherein a load to which electric power is to be supplied is connected to a secondary winding of the transformer.
 16. The wireless power receiving apparatus according to claim 11, wherein the fifth switch through the eighth switch are each configured as a uni-directional switch, and wherein the second control unit is configured to switch on and off the fifth switch through the eighth switch with a phase controlled such that no current flows through each of their inversely conducting elements.
 17. The wireless power receiving apparatus according to claim 11, wherein the fifth switch through the eighth switch are each configured as a bi-directional switch.
 18. The wireless power receiving apparatus according to claim 11, wherein the second control unit is configured to drive the fifth switch through the eighth switch with a predetermined phase difference with respect to a driving voltage applied to a transmission antenna of the wireless power transmitting apparatus.
 19. The wireless power receiving apparatus according to claim 11, wherein the automatic tuning assist circuit is coupled in series with the reception antenna via a transformer.
 20. The wireless power receiving apparatus according to claim 11, wherein the reception antenna comprises a resonance capacitor arranged in series with the reception coil.
 21. A wireless power supply system comprising: a wireless power transmitting apparatus configured to transmit an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field; and the wireless power receiving apparatus according to claim 11, configured to receive the electric power signal.
 22. A wireless power supply system comprising: the wireless power transmitting apparatus according to claim 1; and the wireless power receiving apparatus according to claim 11, configured to receive the electric power signal from the wireless power transmitting apparatus.
 23. An automatic tuning assist circuit employed in a wireless power transmitting apparatus configured to transmit an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field to a wireless power receiving apparatus via a transmission coil, and coupled with the transmission coil, the automatic tuning assist circuit comprising: at least one auxiliary capacitor; four switches arranged in order to charge and discharge the aforementioned at least one auxiliary capacitor using a resonance current that flows through the transmission coil; and a first control unit configured to switch on and off the four switches so as to generate a capacitor voltage across the aforementioned at least one auxiliary capacitor, and to apply, to the transmission coil, a correction voltage that corresponds to the capacitor voltage that develops at the aforementioned at least one auxiliary capacitor.
 24. A wireless power transmitting apparatus configured to transmit an electric power signal comprising any one from among an electric field, a magnetic field, and an electromagnetic field to a wireless power receiving apparatus, the wireless power transmitting apparatus comprising: a transmission antenna comprising a transmission coil; the automatic tuning assist circuit according to claim 23, coupled with the transmission antenna; and a power supply configured to apply an AC driving voltage across a series circuit that comprises the transmission antenna and the automatic tuning assist circuit.
 25. An automatic tuning assist circuit employed in a wireless power receiving apparatus configured to receive an electric power signal comprising any one from among an electric field, a magnetic field, or an electromagnetic field transmitted from a wireless power transmitting apparatus, and coupled with the reception coil, the automatic tuning assist circuit comprising: at least one auxiliary capacitor; four switches arranged in order to charge and discharge the aforementioned at least one auxiliary capacitor using a resonance current that flows through the reception coil; and a second control unit configured to switch on and off the four switches so as to generate a capacitor voltage across of the aforementioned at least one auxiliary capacitor, and to apply, to the reception coil, a correction voltage that corresponds to the capacitor voltage that develops at the aforementioned at least one auxiliary capacitor.
 26. A wireless power receiving apparatus configured to receive an electronic power signal comprising an electric field, magnetic field, or electromagnetic field, transmitted from a wireless power transmitting apparatus, the wireless power receiving apparatus comprises: a reception antenna comprising a reception coil; and the automatic tuning assist circuit according to claim 25, coupled with the reception antenna. 